Why does your blackboard looks white after using it again and againanswer in brief.?

A blackboard appears white after repeated use due to the accumulation of chalk dust and residue from the chalk used for writing. When the board is wiped, the dust can spread, creating a light-colored layer that obscures the original black surface. Additionally, the oils from hands and cleaning materials can contribute to this effect. Over time, the combination of these factors can give the board a faded, lighter appearance.